1. Field of the Invention
The present invention relates to an apparatus for measuring the refractive power of eye and more particularly to such apparatus for refractometry which is able to automatically measure information of eye refractive power including information of astigmatism and which has a video display device to display the measured information in terms of numerals, characters or other symbols.
2. Description of the Prior Art
Eye-refractometers have been used for a long time to examine human eyes and more practically to obtain data for adjustment of spectacles. For this purpose there have been known and proposed various types of eye-refractometers in view of structure and function.
As well known to those skilled in the art, to determine eye refractive power it is required to measure three values, that is, spherical diopter, astigmatism and astigmatic axis. Spherical diopter is diopter in the longitudinal direction in which the diopter is maximum. Astigmatism is changed of diopter with change of the longitudinal direction and astigmatic axis is the longitudinal direction in which diopter is maximum.
In some known eye-refractometers, for example, in those disclosed in U.S. Pat. Nos. 3,883,233 and 3,888,569, the whole optical system or a portion thereof is rotated about its optical axis so that the measuring direction along the longitudinal direction may be changed so as to enable a continuous measurement of eye refractive power along the longitudinal direction.
Also, we, the inventors of the present invention already proposed a novel eye-refractometer in our prior application, U.S. Ser. No. 944,304, now U.S. Pat. No. 4,293,198.
For eye-refractometry it is essential to establish proper alignment of the refractometer to the eye to be examined and to make a correct adjustment of the spacing therebetween. Effective methods for carrying out the necessary adjustment have been proposed in U.S. Pat. Nos. 3,871,772 and 3,864,030 as well as in U.S. Ser. No. 832,829 applied by the same assignee as the present application.
It is also essential to exclude the adverse effect of wink of the eyes on the measurement. If a person under measurement winks his eyes, then it will produce a false result of measurement. For this reason, the above mentioned U.S. Pat. No. 3,888,569 proposed a measuring apparatus in which measurement is stopped during winking of the subject eye. Also, in U.S. Pat. No. 4,149,787 assigned to the assignee of the present application, there has been proposed an eye examining apparatus suitable for detection of winking during measurement.